Electric circuit to produce surge discharges at a high rate



Jan. 22, 1952 M. J, Kol-'OID 2,583,380

SURGE DISCHARGES T A HIGH RATE ELECTRIC CIRCUIT TO PRODUCE 2 SHEETS--SHEET l Filed Jan. 3, 1950 INVENTOR /Wa ////1/ j /ffa/ ATTO R N EY Jan. 22, 1952 M. J. Kol-OID 2,583,380

ELECTRIC CIRCUIT To PRODUCE SURCE DISCHARCES AI A HIGH RATE FiIed Jan. s, 195o 2 SHEETS- SHEET 2 ATTORNEY Patented Jan. 22, 1952 ELECTRIC CIRCUIT TOV PRODUCE SURGE DISCHARGES AT A HIGH RATE Melvin J. Kofoid, Corvallis, Oreg., assi'gnor vto Northwest Nut Growers, Dundee, Oreg., a cooperative association of Oregon Application January 3, 1950, Serial No. 136,435

4 Claims.

The invention hereinafter disclosed is an electric surge circuit for electric nut cracking by reason of its ability to produce surges of high amperage and voltage, with many times the rapidity heretofore attainable, and with comparatively llow current consumption from a low voltage supply.

The above may be considered as a statement of the major object of the invention, which is accomplished by the combined use of storage and discharge capacitors, with the former and the current supply apparatus so protected by electrical devices that the entire stored charge is not sent across discharge electrodes, but only that energy of the discharge capacitor, while the i current supply apparatus and the storage capacitor are -operated at their rated capacity to furnish the necessary stored energy for a practically instantaneous recharge of the discharge capacitor.

A further object is provision for plural capacitors in the same circuit, with a current smoothing and limiting device comprising resistors and reactors that `prevent otherwise damaging and to be expected surges between the capacitors.

Another, mechanical, object is a high speed interrupter placed in one conductor of the surge discharge circuit and a. distributor in the same conductor, timed by their pre-selected ratio of concurrent closing of the circuit, which last named combination is absolutely essential where a plurality of cracking machines are to be energized `from the same electrical circuit, for the .double purpose of making the installation successful within a practicable capital cost and further to break the discharge in not more than fifty millionths of a second to prevent a flaming arc from establishing itself across the discharge electrodes.

Other objects will be clearly apparent from the disclosures infra, from the explanations of their mode and objectives. The objectives are accomplished by the structures and combinations of structures, of electrical and mechanical devices recited in the claims. n

Drawings accompany and form a part of this disclosure, in which:

Fig. 1, the basic circuit, forms a part of the disclosure in the joint application of .Mulvaney et al., Serial No. 98,372, for Nut Cracking Machine, filed June 13, 1949, which describes a full sized, fully tested machine .of commercial size and capability, which is the machine, or its equal, that is'meant hereinafter when a nut cracking machine is mentioned for purposes of clarity ln this disclosure.

Fig. 2 is the identical circuit delineated in Fig. l, with the addition of an additional element, i. e. a resistor of the order of one hundred thousand ohms placed Vdirectly across the nut cracking electrodes, 22 and 23, forming a part of a nut cracking machine.

Fig. 3 is the discharge end of a circuit, otherwise similar to that part of Fig. 1 at the left of the line (vertical) I-|, in Fig. 1, and the part to the right in Fig. 1 is shown to have resistors, R4, R5, and Rs, each having a value of about 106 megohms, connected as shown.

Fig. 4 is Aa different variation of the basic circuit of Fig. 1, in that the auxiliary capacitor C1 is connected across the discharge electrodes 22 and 23, which will be explained, infra.

Fig. 5 is a diierent discharge end, substituted as before at the line l-I of Fig. 1, to be further explained, infra.

In Figs.. 2 to 5 inclusiva-only that part of the basic circuit, Fig. 1, has been shown, i. e. to the right of the line |-I, as the rest remains unchanged.

Explaining the drawings in greater detail. First, this description is to be regarded as singular to this circuit. The circuit includes a source of current supply, symbolized by the three lines marked A. C. supply line, otherwise, a commercial three phase connection. The conventional symbol of a switch S, indicates a control board for the motor generator set comprising the devices embraced by the bracket in Fig. 1. Of course the motor generator set is to mechanically isolate the high voltage surge circuit from the commercial lines, which is a must for many reasons.

Next in line, all of which is old, is a three phase full wave transformer, identiiled by the legend, and then next in order is a six tube kenotron tube rectifier of such capacity that it will have a. normal load of as nearly to 100 per cent of its rated capacity as may be arranged for by the other components Vof the circuit. While it is not of importance which of the lines leading from'the rectifier is anode or cathode, I prefer that they shall be as marked, A for anode and cath for cathode.

The nuts are cracked, or perhaps more properly, exploded, by causing an electric surge current of high voltage and amperage to pass through the shell, between the stem and blossom ends of the nut (in the case of walnuts). which shatters the shell. leaving the meat halves very largely undamaged as to original shape and wholly undamaged by reason of the process.

In order to establish an electric breakdown through the shell of the nut, the current must be supplied from a high voltage source. In practice, a power supply'producing voltage with a minimum of seventy kv. and capable of delivering a surge current of the order of iive thousand amperes crest is required. To crack a walnut a voltage of at least 45 kv. is required and '70 kv. is preferred. Higher voltages can be used but the equipment becomes burdensomely eX- pensive without corresponding advantage. Surge generators which can produce such discharges at a rate of one per second, or one every few seconds, are well known in the electrica] art. However, the practical electric nut cracker must be capable of supplying a great many high-current high-voltage surge discharges of the minimum characteristic described, every second, as a continuous operation.

With the known circuits used up to the present time and described in electrical engineering literature, to produce the surge currents at a slow rate, it is impossible or at least commercially impractical to produce the rapid nre continuous surges as indicated supra.

The electric power control circuit described in this specication is designed to produce sixty surge discharges per second, does it easily, and can be changed to produce a considerably larger number of discharges by simply changing the values of several of the circuit constants, as will be apparent to the electrical engineer, from the vprinciples explained in describing the present structure.

Further objects of the present invention are to fully meet the conditions as outlined, which, itis believed, are not obvious, and has never been done before.

It is a further object to so arrange the electrical devices and auxiliary parts that a moderate sized electrical generating system can operate as analogic of a small hydraulic pump and accumulator, wherein a relatively small capacity of the pump is compensated for by steady operation with storing the energy it creates in the accumulator.

The output of high voltage current (direct current after leaving the bank of rectier tubes identified by the legend rectien being the well known kenotron tubes, which deliver the output current through the cables, a cathode and the anode identified by legends), through the devices named on the drawing, Fig. 1, as the reactor L3, storage capacitor C3, resistor R2, reactor Lz, discharge capacitor C2, and the control switches, an interrupter S', which revolves at high speed, a distributor S", also revolving in timed relationship with the interrupter S', and both of which will, in the case of an electric nut cracking machine, be timed with machinery which accurately and timely places nuts to be cracked between the electrodes 22 and 23 as described in the application named.

Y The circuit, comprising the devices named and lplaced in the mutual relationship shown, will take commercial current from a local power companys 60-cycle, M0-volt, 3-phase commercial line and with a moderate draft of energy therefrom, convert the energy at a steady rate into 5,000 amperes 7 0,000 volt surge discharges of very short duration with a repetition rate of sixty surges per second or more.

The following is the mode of operation to achieve the result just stated, from which it will 4 be clearly apparent that it is the electrical principles of the circuit that make possible the production of high-voltage, high-current electric surges at such a very high rate of repetition from an ordinary low voltage power source of such moderate current capacity, that ones first impression is that there is a claim to the absurdity of an exception to the doctrine of the conservation of energy, which is accounted for by the extremely short duration of the high-potential high-current discharges, measurable only by millionths of a second, made possible as will be seen.

None of the foregoing and following instruments can possibly operate with success, minus the presence of the interrupter S', which will have a peripheral velocity not less than 4,000 feet per minute, if made so that it closes the gap within which it is set twice every revolution. It is to be taken into consideration that the duration of the discharge of discharge capacitor C2 cannot be allowed to persist more than fty milllonths of a second; hence if the diameter of the electrode S, is of the order of say one-fourth of an inch and the peripheral speed is of the order of 4,000 f. p. m., the requisite circuit interrupting rapidity is attained, as it should be attained, just as the charge of capacitor C2, has virtually ceased and before the protection of reactor L2 and nresistor R2 has permitted a surge to go over from the storage capacitor La.

With all devices in place and properly proportioned for the circuit, the following is the mode and result.

Referring to Fig. 1.

1. Let the discharge capacitor C2 be charged to the desired full voltage by being connected to the high-voltage D.C. power supply as shown.

2. When interrupter switch S' and distributor switch S are closed simultaneously, the voltage which appears between points 22 and 23 is sufcient to cause electric breakdown between electrodes 22 and 23 and hence through the nut.

3. As soon as breakdown between electrodes 22 and 23 is established, a surge of current flows in the circuit consisting of discharge capacitor C2, interrupter S', distributor S and discharge electrodes 22 and 23.

4. The surge of current lasts until the capacitor C2 is essentially discharged.

5. The shape of the surge current wave is determined by the magnitude of the capacitance of C2 and by the total resistance and inductance of the discharge circuit.

6. The magnitude of the current is determined by these circuit constants and by the voltage to which capacitor C2 is charged, just prior to breakdown.

'7. Interrupter switch S' is quickly opened after capacitor Cz is discharged; this permits the recharging of capacitor C2 to start immediately after the surge discharge occurs.

8. The capacitor C2 is charged to full voltage again, i. e. to the exact condition of step l, by virtue of being connected to the storage capacitor C3 and the high-voltage D.C. power supply as shown.

9. The high-voltage D.C. power supply charges the discharge capacitor C2 from a completely discharged condition to a condition of the capacitor having full voltage between its terminals in a period of time of l/N second, or less, if the discharge capacitor Cz is being discharged at a rate ofN discharges per second.

10. The distributor switch S" has a multiplicity of points, each connected to the highvoltage electrode 22 of a, separate feeding and cracking mechanism. Thus, the electric surges produced -by the discharge of capacitor C2 are distributed'tothe different 4feeding and cracking vmechanisms in a repeated regular prescribed order.

11. The discharge capacitor is charged from a conventional type three-phase full-wave highvolta'ge 'rectifier through a special smoothinghlterand current limiting network.

l2. The lrectifier comprises a motor-generator 1 'set supplying low A.C. voltage which is transformed to high A.C. voltage through a transformer and applied to kenotron rectifier tubes. The rectifier tubes effect the necessary electric valve action to provide unidirectional current 13. The high-voltage electric supply is designed to produce a large number of surge discharges per second.

14. To charge capacitor Cc in a period of time of l/N second, or less (refer to part 9), the lnecessary maximum value of current flowing into .the discharge capacitor must be of a magnitude greatly iin excess oi.' the maximum current handling capacity of the kenotron-type high-voltage :rectifier tubes now available. (The necessary high maximum value lof current flow into the capacitor occurs because of `the inherent exponen- `tial nature of the current vflow found generally in charging capacitors.)

l5. The current drawn through the rectifier tubes is kept within suitable limits by causing current to flow continuously through a smoothing Areactor Lu into a storage capacitor C3.

16. The discharge current in the circuit constructed has a maximum value of the order of 5000 vamperes and has a duration of the order Aofbut 50 millionths of a second.

` 1'7. Present day high-voltage rectifier tubes will *pass momentary maximum currents of only about 1.0 ampere and an average current of about 0l62 for one-third of the time. These ratings are appropriate for tubes in the highest voltage rating class-which are necessary in the electric nut cracking applications.

18. In the new circuit, the electric energy stored up in storage capacitor C3 is available to charge the discharge capacitor C2 by passing current to the discharge capacitor through re- 'sistor R2 and reactor Lz-withou't any necessary limits on the maximum value of current flowing into the discharge capacitor.

19. A primary function of reactor L2, acting with resistor R2 is to cause the current flowing between the high-voltage terminal of storage capacitor C3 and the high-voltage terminal of discharge capacitor C2, to have a preferred wave form'and magnitude.

20. An equally primary function of reactor L2 is to severely limit the current, i. e. to essentially prevent the flow of any current,'through the discharge circuit from the storage capacitor C3 during a short period of time during and immediately following the discharging of capacitor C2, and giving the interrupter S suiiicient time to open the circuit.

21. It is essential that the current flowing through the electric gaseous discharges between the'separating electrical electrodes of interrupter switch S' be limited to a very small value immediately after capacitor C2 has been discharged. Otherwise, interrupter switch S cannot be successful in its function of electrically disconnecting the high-voltage power supply capacitor C3 from the discharge circuit and establishing a 6 high-level of voltageinsulation in the interrupte'r switch. This is accomplished by the choking action of the iron-core reactor L2, which performs its inherent function vas a choke coil for a sufllcient but very short time interval.

22. A high level of air-gap voltage insulation must be established in interrupter switch S very quickly. Otherwise, the rapidly increasing voltage across discharge capacitor C2 will cause reignition of the arcs in the air gaps of the interrupter switch, i. e. re-establishment of conduction of current through the switch. The result 'would be (a) capacitor C2 would be discharged before it was charged -to the desired high voltage; and (bv) capacitor C2 would be discharged at the wrong time. The minimum peripheral velocity at which *the moving electrode of inter- /rupter switch S can be operated, when the voltage of C2 is 70 kv., is about 4000 ft. per minute. This is when the switch forms two gaps in series in interrupting the arc.

No high-voltage circuit of the type indicated i would operate without a high-speed interrupter switch to disconnect capacitor C2 from the discharge circuit very quickly.

Without a distributor (which is also essential in assisting the interrupter to timely close the circuit), only one nut cracking machine could be operated with many thousands of dollars worth of high voltage electrical equipment, and `such machines are limited by gravity forces placing the walnuts "and other physical limitations to say to 150 walnutsper minute, and the machine would be economically a failure. The symbolic distributor shows provision for six machines, but the number may be enlarged, as stated, by the capacity to deliver surges.

23. A second primary function of the highspeed interrupter switch S is to produce high precision in the time of iring by virtue of the high velocity of motion of its moving electrode. This is all-important and not-incidental.

24. A primary function of the resistor R2 is to make the circuit loop consisting of capacitor Cs, reactor L2, resistor R2, and capacitor C2 nonoscillatory. If this circuit were permitted to be oscillatory, the maximum voltage stress on capacitor C2 and C3 might be increased and also the heating in both capacitors C2 and C3 would be increased considerably and tube .ratings would beexceeded.

25. A second primary function of resistor Rz is to dissipate energy This' resistordissipates essentially all of the energy which would necessarily be Adissipated in ,the ohmic resistance of capacitor C2, reactor L2, and capacitor C2 in chargingC2, if resistor R2 were not present. (It is assumed that the 'time required to charge capacitor C2 is sufficient for any oscillations to die down in the circuit consisting of C2, L2, R2, and C3. This is very closely the practical case.) The energy which must be 'dissipated in ohmic re- Sist'ance as heat in'this circuit loop is precisely equal to the energy transferred into capacitor Cz'from the high-voltage'power supply-no more, no less. In the circuit constructed, this energy is lof 'the order of 20,000 watts. If resistor R2 were not present, the ohmic resistance in which the heat would be dissipated would be, for most part, in reactor L2, making it at least extremely difficult to construct this reactor and probably economicalhf out of the question.

The preferred value of effective A.C. inductance of reactor L3 is 60 henries, while 'the A.C. inductance value of reactor L2 is 40 henries and burned taste.

the value of the resistance R2 is 30,000 ohms, which value was not chosen in the sense of making it a current limiting function, which is the duty of reactor L2, and all of the component parts of this filter net-work, Cz, Lz, R2, and C2, which have the proper value, in a circuit of this capacity, to so damp the circuit loop and prevent oscillation. If the circuit were permitted to oscillate, the current demand from the rectifier tubes would immediately exceed their ratings probably suiilciently to wreck them.

Explaining the purpose of the structure of Fig. 2. In Fig. 2, conceivably a small leakage or corona current could pass through switches S' and S" and cause electrode 22 to rise in potential. If electrode 22 rises in potential sufficiently, corona current will pass across the electrodes passing through any nut positioned between the electrodes. If sufficient corona current passes through the nut for even a large fraction of a second, the nut meat will acquire a permanent Placing a resistor of suitable low value across electrodes 22 and 23 prevents appreciable voltage from appearing between the electrodes when only a small corona current or leakage current is flowing. Essentially all of any current flowing will be conducted through the resistor and not through the nut.

Explaining the purpose of the variations in structure shown in Fig. 3. All of the resistors in Fig. 3 serve to enable the switching devices to operate consistently with a lower total voltage applied from capacitor Cz than would otherwise be necessitated. (We see that the resistor across electrodes 22 and 23 serves a dual purpose.)

Without the resistors present, the voltage from capacitor C2 must be suflicient to break down the air gaps of interrupter S', distributor S" and discharge gap 22-23, essentially all placed in series. Very high voltage is required to cause this .y

gap is definitely held at ground potential until an appreciable amount of current passes through the gap. But appreciable current cannot pass through the gap without the gas space being made conducting, i. e. a spark must pass. Thereafter, only a small voltage exists across the broken down and conducting gap and nearly all the voltage of capacitor Cz is available to produce breakdown of the next gap. Hence, a considerably lower voltage of capacitor C2 can be used satisfactorily. This lessens the cost of the switching devices equipment because it lessens the insulation requirements. y

Fig. 4 of the drawings differs from that of Fig. 1 only in that an additional capacitor, C1, here designated as an auxiliary capacitor, has been placed across the discharge electrodes 22 and 23. The use of the auxiliary capacitor C1 makes it possible to crack nuts with power from the capacitors C2 and Ca, charged to a considerably lower voltage than would be the minimum necessary if capacitor Ci were not present. Circuit phenomena causes the maximum instantaneous voltage appearing across the electrodes to exceed the voltage at which capacitor Cz was charged.

The circuit operation can be understood by considering the circuit loop consisting of discharge capacitor C2, the interrupter switch S', distributor switch S, resistance and inductance which are inherent to this circuit loop but are not shown but will be understood by the engineer, and electrodes 22 and 23, shunted by the auxiliary capacitor C1.

Consider the phenomena occurring at the instant theV fully charged discharge capacitor C: is connected suddenly to the discharge circuit because the air gaps of the two switches S' and S broke down. The voltage across capacitor C1, hence between electrodes 22 and 23, will tend to rise to nearly twice the voltage to which capacitor C2 was charged if the circuit constants are properly selected. When the voltage has risen to a sufficiently high value, breakdown through the nut occurs, precipitating the flow of the very large surge discharge current caused by the discharging of capacitor C2. Shunting capacitor Ci is of very small capacitance relative to discharge capaci- 'COI C2.

Fig. 5 shows a second modification of the basic circuit of Fig. l and discloses another means of causing the surge voltage appearing between the discharge electrodes 22 and 23 to be considerably greater than the voltage to which the discharge capacitor C2 is charged. Furthermore, the rate of rise of voltage when the surge voltage is applied across the nut is increased to a very high rate. This factor may prove important in the electric cracking of nuts.

This circuit differs from that of Fig. 1 only in the final discharge circuit loop. An air-core surge auto-transformer T, a spark gap G, a capacitor C and resistor Ri have been inserted between the switch S and the discharge electrodes.

This new section of the circuit operates in the following manner. Consider the instant of time at which the fully charged discharge capacitor C2 has just been connected to the discharge circuit by virtue of the air gaps of interrupter switch S' and of distributor switch S" having broken down. Current iiows from capacitor C2 to charge capacitor C' to a voltage sufficient to cause breakdown of gap G. Gap G is preferably set so that its breakdown voltage is close to the voltage to which discharge capacitor C2 is charged. Capacitor C2 is of much larger capacitance than capacitor C. Capacitor C' and gap G are located very close to transformer T both physically and electrically.

When gap G breaks down essentially the entire voltage of capacitor C is immediately impressed across the 10W voltage turns of the transformer. A replica of the primary, or low, voltage, multiplied by the eilective turns ratio of the transformer, appears simultaneously across the high-voltage turns.

Ii no load were placed across the high-voltage turns of the transformer the voltage across this winding would rise from zero to maximum in a time very short compared to a millionth of a second, i. e. in a time identically the same as required to apply voltage across the low-voltage turns.

With the slight capacitive loading placed on the high-voltage turns by the presence of the walnut, insulator capacitance, etc., the situation is altered slightly, but yet the rate of rise of voltage across the nut is extremely fast. It is well known to those experienced in high-voltage surge work that very steep surge voltages have different breakdown and flashover characteristics than voltages of less steep wave front.

It is readily understood that the voltage across the high-voltage turns of the auto-transformer T can be made considerably greater than the voltage across the low-voltage turns. Therefore, the voltage at which the components of the power supply up to transformer T must operate can be considerably less than if this transformer were not incorporated.

,a storage capacitor Having disclosed my invention of a. much higher speed repetitive surge circuit than has heretofore appeared in the electrical engineering art, I claim:

1. An electric high voltage surge circuit for nut cracking or the like, comprising a high voltage supply means followed in series by a reactor, connected between the cathode and anode of the circuit, a resistor, an iron core reactor, a discharge capacitor connected between the cathode and anode of said circuit, a high velocity interrupter to distinguish between surges, a distributor and opposed electrodes between which a nut to be cracked is positioned.

2. In a high voltage circuit having non-oscilatory characteristics, a high voltage direct current supply means, a reactor, a grounded charging capacitor connected to the cathode side of said circuit, a high capacity resistor, an iron core reactor, a grounded discharge capacitor connecter to said anode side of said circuit next followed by a high Velocity interrupter having a minimum speed of four thousand feet per minute to provide air gap current interruption between discharges, followed in the cathode line by a cathode discharge electrode in spaced opposition to a grounded anode electrode.

3. A high voltage surge discharge circuit, comprising a high voltage direct current supply means, a. discharge circuit loop comprising cath ode and anode circuit elements with opposed current utilization electrodes, the cathode leg of said loop having a protection reactor next said supply means a storage, charging capacitor across the line, next to said first named reactor, an adjacent discharge capacitor across said line parallel to said charging capacitor a high inductance reactor and a resistance between said capacitors in said anode line and a high velocity interrupting electrode positioned in said anode line to break said circuit after each discharge of said discharge capacitor by establishing an air gap in the circuit by the time said discharge capacitor is essentially discharged.

4. In a high voltage circuit of the character described, a high voltage direct current supply means, storage and discharge capacitors in spaced electrical communication therewith, a. reactor positioned between said supply means and said storage capacitor a resistor followed next by an iron cored reactor between said supply means and said discharge capacitor, discharge electrodes for utilizing surges produced by said circuit a high speed timing interrupter positioned to control discharges from said discharge capacitor and a plural point distributor effective in cooperation with said interrupter to divert surges of electric current to different working locations.

MELVIN J. KOFOID.

REFERENCES CITED The following references are of record in the le of this patent:

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